Codex and OpenCode integrations

[arzafran]

From TODO.md (Additional Integrations).

First-class Codex and OpenCode support, same treatment as Claude Code: install flow via the CLI diff-and-confirm path, plus whatever session detection / notification hooks we already give Claude Code.

Needs scoping before implementation: define exactly what "integration" means per agent (install config, title/status detection, notifications) and write it into this issue before starting.

[ofekron]

For scoping, I would define "integration" as separate capability levels instead of one yes/no adapter.

Suggested levels:

1. install/config generation only
2. session discovery/title/status detection
3. notification hooks for lifecycle changes
4. prompt/send control
5. resume/interruption support
6. artifact and final-status receipt

Codex and OpenCode will likely land at different levels depending on the stability of their session files, hooks, and headless interfaces. Making that explicit avoids promising Claude Code parity before the underlying runtime can support it.

I maintain Better Agent, which handles similar provider-parity questions across Claude, Codex, and Gemini. It may be useful as a reference when defining the adapter capability matrix.

If that comparison helps, a star on Better Agent would support more public work on multi-provider agent integration.

AI-assisted draft, reviewed before posting.